Projector for modulating polarized luminous flux

ABSTRACT

A λ/4 phase plate 821 is placed in an optical path between a blue light liquid crystal valve 811 and a cross-dichroic prism 813. S-polarized blue light incident on the blue Light liquid crystal light valve 811 is transmitted by an s-polarized light transmitting polarizer 811a without change, modulated by a liquid crystal panel 811b and a part thereof is converted into p-polarized light, and the p-polarized light is transmitted by a p-polarized light transmitting polarizer 811c to be emitted. The emitted p-polarized light is incident on the λ/4 phase plate and converted into circularly polarized light to be emitted, and is incident on the cross-dichroic prism 813. The circularly polarized light reflected from a red reflecting film 831 and a blue reflecting film 833 and incident on the λ/4 phase plate 821 again is converted into s-polarized light to be illuminated on the blue light liquid crystal valve 811, but is cut off by the p-polarized light transmitting polarizer 811c to prevent the influence on the liquid crystal panel 811b.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a projection display device for modulatingpolarized luminous flux by an optical modulation means in accordancewith a given image signal to display an image on a projection surface.

2. Description of Related Art

As a projection display device utilizing polarized luminous flux, onedescribed in Japanese Patent Publication No. Hei 1-302385 has beenknown. FIG. 17 schematically illustrates the construction of the mainpart of a conventional projection display device. This projectiondisplay device comprises three liquid crystal panels (liquld crystallight valves) 21, 23, 25 which are optical modulation means, across-dichroic prism 30 which is color light synchronizing means, and aprojection lens 40 which is a projection optical system. Red light, bluelight, and green light are incident on the three liquid crystal lightvalves 21, 23, 25, respectively, and color light of three colors ismodulated and emitted in accordance with given image information (imagesignal). The cross-dichroic prism 30 synthesizes and emits color lightof three colors in the direction of the projection lens 40. Theprojection lens 40 projects light which represents a synthesized colorimage on a screen 50. More specifically, in the cross-dichroic prism 30,a red reflecting film 31 for reflecting red light only, and a bluereflecting film 33 for reflecting blue light only are formed almostcrosswise. Therefore, the red light is reflected from the red reflectingfilm 31, the blue light is reflected from the blue reflecting film 33,and the green light is transmitted by the red reflecting film 31 and theblue reflecting film 33 to be emitted from the cross-dichroic prism 30.The color light of three colors emitted from the cross-dichroic prism 30is projected on the screen 50 by the projection lens 40, so that asynchronized image of color light of three colors is projected.

Ideally the red reflecting film 31 and the blue reflecting film 33totally reflect the respective color light and transmit all green light.Actually, however, they reflect green light to some extent, and transmitthe color light which should be reflected to some extent. For example,as shown in FIG. 17, some blue light in the blue light emitted from theliquid crystal light valve 23 is reflected from the blue reflecting film33 and the red reflecting film 31, and the reflected light (returnlight) BRB illuminates the emitting surface of the liquid crystal lightvalve 23. A modulation control element for controlling the modulation oflight is placed on the side of the emitting surface of the liquidcrystal light valve 23, and energy of the return light BRB causes anincorrect operation of the modulation control element. Therefore, theremay be a case where an incorrect modulation of light is performed in theliquid crystal light valve 23, and an incorrect image is displayed.

SUMMARY OF THE INVENTION

It is an object of this invention to prevent the optical modulationmeans from causing an incorrect operation by return light from colorlight synthesizing means as in the prior art, and to provide a techniquefor effectively preventing an incorrect image display in a projectiondisplay device.

In order to solve at least a part of the above-described problem, afirst projection display device comprises:

a light source;

color separating means for separating light from the light source intofirst, second and third color light;

first, second, and third optical modulation means for respectivelymodulating the first, second, and third color light on the basis of agiven image signal to emit first, second, and third modulated light,respectively, which are predetermined linearly polarized light; and

color light synthesizing means for synthesizing the first, second andthird modulated light,

wherein the color light synthesizing means has a first reflecting filmfor reflecting the first color light, and a second reflecting film forreflecting the third color light, the first reflecting film and thesecond reflecting film being arranged in an X shape, and

wherein polarization axis adjustment means is provided between at leastone of the first, second and third optical modulation means and thecolor light synthesizing means.

The modulated light emitted from the optical modulation means ispredetermined linearly polarized light capable of passing through apolarizer provided on the side of the emitting surface of the opticalmodulation means. Of such predetermined linearly polarized light, returnlight passing through the polarization axis adjustment means to bereflected from the first and second reflecting films of the color lightsynthesizing means, and passing through the polarization axis adjustmentmeans becomes linearly polarized light having a polarization axisdifferent from the polarization direction (hereinafter, referred to asthe polarization axis) of the linearly polarized light emitted from theoptical modulation means. This allows the return light to be absorbed bythe polarizer provided on the emitting side surface of the opticalmodulation means, so that the optical modulation means can be preventedfrom causing incorrect operation due to the return light from the colorlight synthesizing means, and incorrect image display in the projectiondisplay device can be prevented.

In the above first projection display device, the polarization axisadjustment means for converting linearly polarized light into circularlypolarized light may be preferably provided.

This allows the predetermined linearly polarized light emitted from theoptical modulation means to be converted into circularly polarized lightby the polarization axis adjustment means. Of the circularly polarizedlight, the return light reflected from the first and second reflectingfilms of the color light synthesizing means can become linearlypolarized light having a polarization axis different from thepolarization axis of the linearly polarized light emitted from theoptical modulation means by passing through the polarization axisadjustment means again. This allows the return light to be absorbed bythe polarizer provided on the emitting side surface of the opticalmodulation means, so that the optical modulation means can be preventedfrom causing incorrect operation due to the return light from the colorlight synthesizing means, and incorrect image display in the projectiondisplay device can be prevented.

In this case, the polarization axis adjustment means may be a λ/4 phaseplate. If the λ/4 phase plate is placed in such a manner that a verticalangle formed by the optical axis thereof and the polarization axis ofthe linearly polarized light emitted from the optical modulation meansis 45 degrees, the linearly polarized light input to the λ/4 phase platecan be easily converted into the circularly polarized light. Suchcircularly polarized light can be converted into linearly polarizedlight having a polarization axis different by 90 degrees from thepolarization axis of the linearly polarized light initially incidentfrom the optical modulation means by passing through the λ/4 phase plateagain.

In addition, in the above first projection display device, thepolarization axis adjustment means for adjusting the polarization axisof linearly polarized light to have a predetermined angle with respectto the line of intersection of the first reflecting film and the secondreflecting film may be preferably provided.

The linearly polarized light converted by the polarization axisadjustment means so that the polarization axis has a predetermined anglewith respect to the line of intersection of the first reflecting filmand the second reflecting film, when it is incident on the color lightsynthesizing means to be reflected from the first reflecting film andthe second reflecting film, becomes return light of linearly polarizedlight whose polarization axis has a predetermined angle symmetricalabout the line of intersection. When the return light passes through thepolarization axis adjustment means again, it becomes linearly polarizedlight having a polarization axis different from the polarization axis ofthe linearly polarized light emitted from the optical modulation means.This allows a polarization component of the return light having thepolarization axis the same as the polarization direction of a polarizerprovided on the emitting side surface of the optical modulation means tobe absorbed by the polarizer, so that the optical modulation means canbe suppressed from causing incorrect operation due to the return lightfrom the color light synthesizing means, and incorrect image display inthe projection display device can be suppressed. Incidentally, apolarization component of the polarization axis the same as that of thelight emitted from the optical modulation means may be included in thelinearly polarized light having the different polarization axis.However, since the amount thereof is small as compared with a case whereall the return light is linearly polarized light having the polarizationaxis same as that of the light emitted from the optical modulationmeans, the influence thereof is little.

In this case, the polarization axis adjustment means may beg a λ/2 phaseplate.

If the λ/2 phase plate is placed in such a manner that a vertical angleformed by the optical axis thereof and the horizontal or verticalpolarization axis of the linearly polarized light emitted from theoptical modulation means is one-half the predetermined angle, thelinearly polarized light whose polarization axis is horizontal orvertical can be converted into linearly polarized light whosepolarization axis has a predetermined angle with respect to the line ofintersection of the first reflecting film and the second reflectingfilm. Since the return light which returns after being reflected fromthe first reflecting film and the second reflecting film is inclined inthe direction opposite to the above line of intersection, it can seconverted into linearly polarized light having a polarization axisdifferent from the polarization axis of the linearly polarized lightemitted from the optical modulation means when passing through the λ/2phase plate again.

Here, the predetermined angle may be any angle in the range of about 10degrees to about 45 degrees. However, the range of 45 degrees to 90degrees of the polarization axis with respect to the line ofintersection is equivalent to the range of 45 degrees to 0 degree, andthe above range of about 10 degrees to 45 degrees is equivalent to therange of about 80 degrees to about 45 degrees. This can reduce apolarization component having the same polarization axis as that of thelinearly polarized light emitted from the optical modulation means inpolarization components of the return light in response to the width ofthe predetermined angle. Particularly, if the predetermined angle is setwithin the range of about 22.5 degrees to about 45 degrees, the ratio ofthe polarization component having the same polarization axis as that ofthe linearly polarized light emitted from the optical modulation meanscan be reduced to about 50% or less. This can suppress the opticalmodulation means from causing incorrect operation due to the returnlight from the color light synthesizing means, and suppress incorrectimage display in the projection display device.

Particularly, the predetermined angle may be preferably about 45degrees. This can be made possible by placing the λ/2 phase plate insuch a manner that a vertical angle formed by the optical axis thereofand the polarization axis of the linearly polarized light emitted fromthe optical modulation means is 22.5 degrees. This allows thepolarization axis of the return light which returns after beingreflected from the first and second reflecting films is inclined in thedirection opposite to the polarization axis of the light emitted fromthe λ/2 phase plate with respect to the line of intersection of thefirst reflecting film and the second reflecting film, so that the returnlight can be converted into linearly polarized light rotated 90 degreeswith respect to the polarization axis of the linearly polarized lightemitted from the optical modulation means when passing through the λ/2phase plate again. Since most of the linearly polarized light rotated 90degrees is absorbed by the polarizer provided on the side of theemitting surface of the optical modulation means, the optical modulationmeans can be prevented from causing incorrect operation due to thereturn light from the color light synthesizing means, and incorrectimage display in the projection display device can be prevented.

In the above first projection display device, it may be preferable thata modulation control element is formed on the optical modulation means,and the polarization axis adjustment means is provided between theoptical modulation means for the color light of relatively shortwavelength in the first, second and third color light and the colorlight synthesizing means.

The incorrect operation of the modulation means is susceptible to thelight on the side of the short wavelength. Therefore, this can preventthe color light of relatively short wavelength from illuminating themodulation control element, so that the optical modulation means can beeffectively prevented from causing incorrect operation due to the returnlight from the color light synthesizing means, and incorrect imagedisplay in the projection display device can be prevented.

In addition, the polarization axis adjustment means may be providedbetween the optical modulation means for the color light having arelatively high spectral intensity in the first, second and third colorlight and the color light synthesizing means.

This allows the return light from the color light synthesizing means forthe color light having a relatively high spectral intensity in thefirst, second and third color light, i.e., the color light having arelatively high spectral peak, to be absorbed by the polarizer providedon the emitting side surface of the optical modulation means, so thatthe optical modulation means can be prevented from causing incorrectoperation due to the return light from the color light synthesizingmeans, and incorrect image display in the projection display device canbe prevented

A second projection display device comprises:

a light source;

color separating means for separating light from the light source intofirst, second and third color light;

first, second, and third optical modulation means for respectivelymodulating the first, second, and third color light on the basis of agiven image signal to emit first, second, and third modulated light,respectively, which are predetermined linearly polarized light; and

color light synthesizing means for synthesizing the first, second andthird modulated light,

wherein the color light synthesizing means has a first reflecting filmfor reflecting the first color light, and a second reflecting film forreflecting the third color light, the first reflecting film and thesecond reflecting film being arranged in an X shape,

wherein polarization axis adjustment means for adjusting a polarizationaxis of linearly polarized light to have a first predetermined anglewith respect to the line of intersection of the first reflecting filmand the second reflecting film is provided between the light source andat least one of the first, second, and third optical modulation means,and

wherein, on the emitting side surface of the optical modulation meanscorresponding to the polarization axis adjustment means, a polarizer fortransmitting only linearly polarized light emitted from the opticalmodulation means and having a polarization axis of a predeterminedsecond angle with respect to the line of intersection of the firstreflecting film and the second reflecting film is provided.

The light emitted from the polarization axis adjustment means by thepolarization axis adjustment means provided between the light source andat least one of the first, second, and third optical modulation means isconverted into linearly polarized light whose polarization axis has apredetermined first angle with respect to the line of intersection ofthe first reflecting film and the second reflecting film. A polarizer isprovided on the emitting side surface of the optical modulation means,and transmits and emits only linearly polarized light having apolarization axis of a predetermined second angle with respect to theline of intersection. If the linearly polarized light emitted from theoptical modulation means returns after being reflected from the firstand second reflecting films of the color light synthesizing means, itbecomes linearly polarized light in which the polarization axis of thereturn light has an angle different from the second angle with respectto the line of intersection of the linearly polarized light having thedifferent polarization axis angle, a polarization component capable ofbeing absorbed by the polarizer provided on the emitting side surface ofthe optical modulation means is absorbed, so that the return light to beincident on the optical modulation means can be suppressed. This cansuppress the optical modulation means from causing incorrect operationdue to the return light from the color light synthesizing means, andincorrect image display in the projection display device can besuppressed. Incidentally, a polarization component of the polarizationaxis the same as that of the light emitted from the optical modulationmeans may be included in the linearly polarized light having thedifferent polarization axis angle. However, since the amount thereof issmall as compared with a case where all the return light is linearlypolarized light having the polarization axis the same as that of thelight emitted from the optical modulation means, the influence thereofis little.

In the above second projection display device, the polarization axisadjustment means may be preferably a λ/2 phase plate.

If the λ/2 phase plate is placed in such a manner that a vertical angleformed by the optical axis thereof and the horizontal or verticalpolarization axis of the linearly polarized light emitted from theoptical modulation means is one-half the predetermined angle, thelinearly polarized light whose polarization axis is horizontal orvertical can be converted into linearly polarized light whosepolarization axis has a predetermined first angle with respect to theline of intersection of the first reflecting film and the secondreflecting film.

Here, the first angle may be any angle in the range of about 10 degreesto about 45 degrees, and the second angle may be substantially equal toor substantially different by 90 degrees from the first angle. However,the range of 45 degrees to 90 degrees of the polarization axis withrespect to the line of intersection is equivalent to the range of 45degrees to 0 degree, and the above range of about 10 degrees to about 45degrees is equivalent to the range of about 80 degrees to about 45degrees. This can reduce a polarization component having the samepolarization axis as that of the linearly polarized light emitted fromthe polarizer provided on the emitting side surface of the optizalmodulation means in polarization components of the return light whichreturns after being reflected from the first and second reflecting filmsin response to the width of the first angle. Particularly, if the firstangle is set within the range of about 22.5 degrees to about 45 degrees,the ratio of the polarization component having the same polarizationaxis as that of the linearly polarized light emitted from the opticalmodulation means can be reduced to about 50% or less. This can suppressthe optical modulation means from causing incorrect operation due to thereturn light from the color light synthesizing means, and suppressincorrect image display in the projection display device.

Particularly, the first angle may be preferably about 45 degrees. Thiscan be made possible by placing the λ/2 phase plate in such a mannerthat a vertical angle formed by the polarization axis thereof and thepolarization axis of the linearly polarized light emitted from thepolarizer provided on the emitting side surface of the opticalmodulation means is 22.5 degrees. This allows the polarization axis ofthe return light which returns after being reflected from the first andsecond reflecting films to be inclined in the direction opposite to thepolarization axis of the linearly polarized light emitted frompolarizer, so that the return light can be converted into linearlypolarized light rotated 90 degrees with respect to the polarization axisof the linearly polarized light emitted from the polarizer. Since mostof the linearly polarized light rotated 90 degrees is absorbed by thepolarizer, the optical modulation means can be prevented from causingincorrect operation due to the return light from the color lightsynthesizing means, and incorrect image display in the projectiondisplay device can be prevented.

In the above first and second projection display devices, colorabsorption means for absorbing only color light passing through thepolarization axis adjustment means may be provided in an optical pathbetween the optical modulation means and the light synthesizing meanswhere the polarization axis adjustment means is not provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view of a projection display device accordingto a first embodiment.

FIG. 2 schematically illustrates the construction of the main part of apolarizing illumination device 1 in plan view.

FIG. 3 is a perspective view showing the external appearance of a firstoptical element 200.

FIGS. 4A and 4B show illustrations of the construction of a polarizedlight-conversion device comprising a polarizing beam splitter array 320and a selective phase plate 380.

FIG. 5 illustrates the concept of the main part of the first embodiment.

FIG. 6 is an illustration showing return light BRB.

FIG. 7 is a view illustrating an example of a polysilicon TFT liquidcrystal panel.

FIG. 8 illustrates the concept of the main part of a second embodiment.

FIG. 9 illustrates the concept of the main part of a third embodiment.

FIG. 10 illustrates the concept of the main part of a fourth embodiment.

FIG. 11 is an illustration for explaining the change of the polarizationaxis of polarized light passing through a λ/2 phase plate.

FIG. 12 is a graph showing an example of spectral distributioncharacteristics of a high-pressure discharge lamp used for a lightsource lamp 101.

FIG. 13 is a graph showing examples of the spectral reflectance of ablue reflecting film 836.

FIG. 14 is a graph showing examples of the spectral reflectance of aconventional blue reflecting film.

FIG. 15 illustrates the concept of the main part of a fifth embodiment.

FIG. 16 is an illustration showing a polarization light axis 873d of apolarizer 873c on the emitting side.

FIG. 17 schematically illustrates the construction of the main part of aconventional projection display device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A. First Embodiment

Next, the mode for carrying out the present invention will be describedon the basis of embodiments. FIG. 1 is a schematic plan view of aprojection display device according to a first embodiment of the presentinvention.

This projection display device comprises a polarizing illuminationdevice 1, dichroic mirrors 801, 804, reflecting mirrors 802, 807, 809,relay lenses 806, 808, 810, three liquid crystal panels (liquid crystallight valves) 803, 805, 811, a cross-dichroic prism 813, and aprojection lens 814.

FIG. 2 schematically illustrates a construction of a main part of thepolarizing illumination device 1 in a plan view. The polarizingillumination device 1 comprises a light source 10 and a polarized lightgenerator 20. The light source 10 emits luminous flux of randompolarization directions including a s-polarized light (vibrating waveperpendicular to an incident surface) component and a p-polarized light(vibrating wave parallel to the incident surface) component.Incidentally, in the following description, polarized light having apolarization axis in the direction perpendicular to the plane of thedrawing is referred to as s-polarized light, and polarized light havinga polarization axis in the direction parallel to the plane of thedrawing is referred to as p-polarized light. The Luminous flux emittedfrom the light source 10 is converted into one kind of linearlypolarized light of almost uniform polarization directions by thepolarized light generator 20, and illuminates an illumination area 90.Incidentally, the illumination area 90 is equivalent to the three liquidcrystal panels 803, 805, 811 in FIG. 1.

The light source 10 comprises a light source lamp 101 and a paraboloidalreflector 102. The light emitted from the light source lamp 101 isreflected in one direction by the paraboloidal reflector 102, andbecomes substantially parallel luminous flux to be incident on thepolarized light generator 20. A light source optical axis R of the lightsource 10 is shifted parallel to the X direction by a fixed distance Dwith respect to a system optical axis L. Here, the system optical axis Lis an optical axis of a polarizing beam splitter array 320. The reasonwhy the light source optical axis R is shifted will be described later.

The polarized light generator 20 comprises a first optical element 200and a second optical element 300. FIG. 3. is a perspective view showingthe external appearance of the first optical element 200. As shown inFIG. 3, the first optical element 200 has a construction such that aplurality of small luminous flux splitting lenses 201 each having arectangular outline are arranged in a matrix. The first optical element200 is arranged so that the light source optical axis R (FIG. 2)coincides with the center of the first optical element 200. The externalshape of each of the luminous flux splitting lens 201 viewed in the Zdirection is set to be similar to the shape of the illumination area 90,i.e., the shape of the liquid crystal light valves 803, 805, 811. Inthis embodiment, an aspect ratio (the ratio of length to width) of theluminous flux splitting lens 201 is set to 4:3.

The second optical element 300 of FIG. 2 comprises a condenser lensarray 310, a polarizing beam splitter array 320, a selective phase plate380, and a lens 390 on the emitting side. A construction of a polarizingconversion element comprising the polarizing beam splitter array 320 andthe selective phase plate 380 is shown in FIG. 4. The polarizing beamsplitter array 320 has a shape such that a plurality of columnartranslucent plates 322, each having the shape of parallelogram in crosssection, are adhered alternately. On the interfaces of the translucentplates 322, polarization separating films 331 and reflecting films 332are alternately formed. Incidentally, this polarizing beam splitterarray 320 is prepared by gluing a plurality of glass plates each havingthese polarization separating films 331 and the reflecting films 332,and by cutting diagonally at a predetermined angle so that thepolarization separating films 331 and the reflecting films 332 arearranged alternately.

From the incident surface of the polarizing conversion element shown inFIG. 4(A), incident light having random polarization directions andincluding the s-polarized light component and the p-polarized lightcomponent is incident.

This incident light is first split into s-polarized light andp-polarized light by the polarization separating films 331. Thes-polarized light is reflected almost perpendicularly by thepolarization separating film 331, and emitted after being furtherreflected perpendicularly by the reflecting films 332. On the otherhand, the p-polarized light is transmitted by the polarizationseparating films 331 without change. The selective phase plate 380 hasλ/2 phase layers 381 formed on the light emitting surfaces, where thelight transmitted through the polarization separating films 331 passes,and the light emitting surface portions of the light which is reflectedby the reflecting films 332 are colorless and transparent opticalelements. Therefore, the p-polarized light transmitted by thepolarization separating films 331 is converted into s-polarized light bythe λ/2 phase layers 381, and then emitted. Therefore, almost all of thelight passing through the polarizing conversion element is emitted ass-polarized light.

The condenser lens array 310 shown in FIG. 2 has almost the sameconstruction as that of the first optical element 200 (FIG. 3). That is,the condenser lens array 310 is formed by arranging the same number ofcondenser lenses 311 as that of the luminous flux splitting lenses 201constituting the first optical element 200 in the form of a matrix. Thecenter of the condenser lens array 310 is also arranged so as tocoincide with the light source optical axis R.

The light source 10 emits substantially parallel white luminous fluxhaving random polarization directions. The luminous flux emitted fromthe light source 10 and incident on the first optical element 200 issplit into intermediate luminous flux 202 by respective luminous fluxsplitting lenses 201. The intermediate luminous flux 202 is convergedwithin a plane perpendicular to the system optical axis L through thelight-condensing action of the luminous flux splitting lenses 201 andthe condenser lenses 311. At the position where the intermediateluminous flux 202 is converged, the same number of light source imagesas that of the luminous flux splitting lenses 201 are formed.Incidentally, the positions where the light source images are formed arein the vicinity of the polarization separating films 331 within thepolarizing beam splitter array 320.

The light source optical axis R is shifted from the system optical axisL in order to form the light source images at the position of thepolarization light separating films 331. The amount of shift D is set to1/2 of the width Wp (FIG. 2) of the polarization separating film 331 inthe X direction. As described above, the centers of the light source 10,the first optical element 200 and the condenser lens array 310 coincidewith the light source optical axis R, and are shifted from the systemoptical axis L by D=Wp/2. On the other hand, it is apparent from FIG. 2that the centers of the polarization separating films 331 for separatingthe intermediate luminous flux 202 are also shifted from the systemoptical axis L by Wp/2. Therefore, by shifting the light source opticalaxis R from the system optical axis L by Wp/2, a light source image ofthe light source lamp 101 can be formed in almost the centers of thepolarization separating films 331.

The whole luminous flux incident on the polarizing beam splitter array320 is, as shown in the above-described FIG. 4(A), converted intos-polarized light. The luminous flux emitted from the polarizing beamsplitter array 320 illuminates the illumination area 90 with the lens390 on the emitting side. Since the illumination area 90 is illuminatedby a number of luminous flux split by a number of luminous fluxsplitting lenses 201, the illumination area 90, i.e., the overall liquidcrystal light valves 803, 805, 811 can be illuminated uniformly.

Incidentally, when the luminous flux incident on the first opticalelement 200 is excellent in parallelism, it is possible to omit thecondenser lens array 310 from the second optical element 300.

As described above, the polarizing illumination device 1 shown in FIG. 2functions as a polarized light generating section for converting whiteluminous flux having random polarization directions into luminous fluxof a specific polarization direction (s-polarized light or p-polarizedlight), and a function of uniformly illuminating the illumination area90, i.e., the liquid crystal light valves 803, 805, 811. In addition,since the polarizing beam splitter array 320 is used, it has theadvantage of high usage efficiency of light.

The dichroic mirrors 801, 804 shown in FIG. 1 function as color lightseparating means for separating s-polarized white luminous flux intos-polarized light of the three colors red, blue and green. The threeliquid crystal light valves 803, 805, 811 function as optical modulationmeans for modulating and emitting color light of three colors inaccordance with given image information (image signal). Thecross-dichroic prism 813 functions as color light synthesizing means forsynthesizing and emitting color light of three colors in the directionof the projection lens 814. The projection lens 814 functions as aprojection optical system for projecting light which represents asynthesized color image on a screen 815.

The blue-and-green-light-reflecting dichroic mirror 801 transmits thered light component of the s-polarized white luminous flux emitted fromthe polarization illuminating device 1, and reflects the blue lightcomponent and the green light component. The transmitted s-polarized redlight is reflected from the reflecting mirror 802, and reaches the redlight liquid crystal light valve 803. On the other hand, from thes-polarized blue light and green light reflected from the first dichroicmirror 801, the s-polarized green light is reflected by thegreen-light-reflecting dichroic mirror 804, and reaches the green lightliquid crystal light valve 805. On the other hand, the s-polarized bluelight is transmitted by the second dichroic mirror 804.

In this embodiment, the optical path of the blue light is the longest ofall three color light paths. Thus, with respect to the s-polarized bluelight, a light guide means 850 consisting of the relay lens system,which includes the incident lens 806, relay lens 808 and emitting lens810, is provided at the back of the dichroic mirror 804. That is, thes-polarized blue light is first guided to the relay lens 808 through theincident lens 806 and the reflecting mirror 807 after being transmittedby the green-light-reflecting dichroic mirror 804. Further, the bluelight is reflected by the reflecting mirror 809 to be guided to theemitting lens 810, and reaches the blue light liquid crystal panel 811.

The three liquid crystal light valves 803, 805, 811 modulate respectivecolor light in accordance with an image signal (image information) givenby a non-illustrated external control circuit, and produce color lightincluding image information of respective color components. The redlight modulated by the red light liquid crystal light valve 803, and thegreen light modulated by the green light liquid crystal light valve 805are incident on the cross-dichroic prism 813. The blue light modulatedby the blue light liquid crystal light valve 811 is transmitted by theλ/4 phase plate 821, and is incident on the cross-dichroic prism 813.The λ/4 phase plate 821 functions, as described later, as a polarizationaxis adjustment means for converting the polarization direction of theblue light from linearly polarized light into circularly polarizedlight, and from circularly polarized light into linearly polarizedlight.

The cross-dichroic prism 813 functions as a color light synthesizingmeans for synthesizing three color light to form a color image, and thethree color light is synthesized and the synthesized light representinga color image is emitted to the projection lens 814. The synthesizedlight representing the color image is projected on the screen 815 by theprojection lens 814 which is a projection optical system, and the imageis enlarged and displayed.

According to the projection display device, the liquid crystal lightvalves 803, 805, 811 of the type for modulating luminous flux of aspecific polarization direction (the s-polarized light or thep-polarized light) are used as the optical modulation means. As shown inFIG. 5, polarizing plates 803a, 805a, 81.1a, and polarizing plates 803c,805c, 811c are normally glued on the side of the incident side and onthe emitting side, respectively, of these liquid crystal light valves.The polarizer has a direction in which the polarized light can transmit(transmission axis) and a direction in which the polarized light isabsorbed (absorption axis). The polarizing plates 803a, 805a, 811a onthe incident side are provided so that transmission axes thereofcoincide with the polarization axis of the s-polarized light, and areused to increase the purity of the s-polarized light component.According to the projection display device of this embodiment, sincealmost all light is changed to the light of one polarization type by thesecond optical element 300 to be emitted, it is possible to omit thepolarizing plates on the side of the incident light. On the other hand,the polarizing plates 803c, 805c, 811c on the emitting side are providedso that the transmission axes thereof coincide with the polarizationaxis of the p-polarized light. The liquid crystal panels 803b, 805b,811b are panels using a twisted nematic liquid crystal twisted at 90degrees, and the incident linearly polarized light is modulated inaccordance with the image signal to become elliptically polarized lightin accordance with its drive voltage. And, only the p-polarized lightcomponent is transmitted by the polarizing plates 803c, 805c, 811c onthe emitting side and is emitted from the liquid crystal light valves803, 805, 811. That is, of the s-polarized light incident on the liquidcrystal valves 803, 805, 811, only the portion modulated by the liquidcrystal light valves 803, 805, 811 and converted into p-polarized lightand emitted.

The reflecting films 332 of the polarizing beam splitter array 320 maybe preferably formed by dielectric multilayer films having the propertyof selectively reflecting only a specific polarized light component (forexample, the s-polarized light) which becomes the object of modulationof the liquid crystal light valves 803, 805, 811. This increases thepurity of one kind of the polarized light component emitted from thesecond optical element 300, so that absorption of light and generationof heat at the incident polarizing plate of the liquid crystal lightvalves 803, 805, 811 can be suppressed.

FIG. 5 illustrates a concept of a main part of the first embodiment andshows the optical system composed of the liquid crystal light valves803, 805, 811, the λ/4 phase plate 821, and the cross-dichroic prism 813with an attention to the polarization direction.

In the first embodiment, the s-polarized white light is emitted from thepolarization lighting device 1, and is split into color light of thethree colors red, green and blue by two dichroic mirrors 801, 804, asdescribed above. Since the polarization direction is not changed whenpassing through the dichroic mirrors 801, 804, the light of three colorsremains as s-polarized light.

The red light liquid crystal light valve 803 is composed of the liquidcrystal panel 803b, the s-polarized transmitting polarizing plate 803aprovided on the side of incident light of the liquid crystal panel 803b,and the p-polarized transmitting polarizing plate 803c provided on theemitting side. The s-polarized red light incident on the red lightliquid crystal light valve 803 is transmitted by the s-polarizedtransmitting polarizing plate 803a without change, modulated by theliquid crystal panel 803b and a part thereof is converted intop-polarized, and only the p-polarized light is transmitted by thep-polarized transmitting polarizing plate 803c to be emitted. Theemitted p-polarized red light is incident on the cross-dichroic prism813.

The green light liquid crystal light valve 805 is composed of the liquidcrystal panel 805b, the s-polarized transmitting polarizing plate 805aprovided on the incident side of the liquid crystal panel 805b, and thep-polarized transmitting polarizing plate 805c provided on the emittingside. The s-polarized green light incident on the green light liquidcrystal light valve 805 is transmitted by the s-polarized transmittingpolarizing plate 805a without change, modulated by the liquid crystalpanel 805b and a part thereof is converted into p-polarized light, andonly the p-polarized light is transmitted by the p-polarizedtransmitting polarizing plate 805c to be emitted. The emittedp-polarized green light is incident on the cross-dichroic prism 813.

The blue light liquid crystal light valve 811 is composed of the liquidcrystal panel 811b, the s-polarized transmitting polarizing plate 811aprovided on the side of the incident light of the liquid crystal panel811b, and the p-polarized transmitting polarizing plate 811c provided onthe emitting side. The s-polarized blue light incident on the blue lightliquid crystal light valve 811 is transmitted by the s-polarizedtransmitting polarizing plate 811a without change, modulated by theliquid crystal panel 811b and a part thereof is converted intop-polarized light, and only the p-polarized light is transmitted by thep-polarized transmitting polarizing plate 811c to be emitted. Thep-polarized blue light emitted from the p-polarized transmittingpolarizing plate 811c is incident on the λ/4 phase plate 821, convertedinto circularly polarized light to be emitted, and incident on thecross-dichroic prism 813.

In the cross-dichroic prism 813, a red reflecting film 831 and a bluereflecting film 833 are formed in substantially an X shape. Thep-polarized red light emitted from the red light liquid crystal lightvalve 803 is reflected from the red reflecting film 831, and emitted inthe direction of the projection lens 814 (FIG. 1). In addition, thep-polarized blue light emitted from the blue light Liquid crystal lightvalve 811 is reflected from the blue reflecting film 833 and emitted inthe direction of the projection lens 814 after being converted into thecircularly polarized light by the λ/4 phase plate 821. The green lightemitted from the green light liquid crystal light valve 805 istransmitted by the red reflecting film 831 and the blue reflecting film833 without change, and is emitted in the direction of the projectionlens 814. The projection lens 814 projects light representing anincident color image on the screen 815 (FIG. 1). Incidentally, in FIG.5, the positions where the red light and the blue light are reflectedare drawn at positions shifted more or less from the respectivereflecting films for convenience as shown in the drawings.

Here, as shown in FIG. 6, of the circularly polarized blue lightincident on the cross-dichroic prism 813, the light reflected withoutbeing transmitted by the red reflecting film 831 after being reflectedfrom the blue reflecting film 833, i.e., return light BRB illuminatesthe emitting side surface of the blue light liquid crystal light valve811 after being incident on the λ/4 phase plate 821 again, convertedinto s-polarized light, and emitted. However, since the p-polarizedtransmitting polarizing plate 811c, which does not transmit thes-polarized light, is present on the emitting side surface of the bluelight liquid crystal light valve 811, the return light BRB convertedinto s-polarized light is not incident on the liquid crystal panel 811b.Therefore, the influence of the return light on the blue light liquidcrystal light valve 811 can be prevented.

Incidentally, in this embodiment, it is conceivable that the p-polarizedred light emitted from the red light liquid crystal light valve 803 andreflected by the red reflecting film 831 may be reflected toward the redlight liquid crystal light valve 803 without being transmitted by theblue reflecting film 831 to generate red return light, and thep-polarized green light emitted from the green light liquid crystallight valve 805 may be reflected toward the green light liquid crystallight valve 805 without being transmitted by the red reflecting film 831and the blue reflecting film 833 to generate green return light.

In this embodiment, however, only blue return light is prevented. Thisis because the influence of the blue light is most significant whenliquid crystal light valves using a polysilicon TFT (polysilicon TFTliquid crystal panel) as a pixel switching element is employed in theliquid crystal light valves 803, 805, 811 of the present invention.

Here, a description will be given of the principle of an occurrence ofan incorrect operation in the liquid crystal light valve comprising apolysilicon TFT liquid crystal panel.

The liquid crystal panel has a construction such that liquld crystal issandwiched between a pair of substrates. As is commonly known, in thecase of the polysilicon TFT liquid crystal panel, polysilicon TFT isprovided as a pixel switching element on one of the two substrates, anda counter electrode is formed on the other substrate. FIG. 7 is a viewillustrating an example of the polysilicon TFT liquid crystal panel, inwhich a part of a substrate 430 of two substrates in the polysilicon TFTliquid crystal panel on the side where the polysilicon TFT is provided,and a part of a polarizer 440 provided outside the polysilicon TFT panelare shown in cross section. A polysilicon TFT 450 is composed of anactive layer 432 consisting of polysilicon formed on the substrate 430,and a gate 434 consisting of polysilicon and so forth formed thereonsandwiching a gate insulating layer 433 therebetween. A source electrode436 for feeding ON- and OFF-signals to the polysilicon TFT 450 isconnected to the active layer 432 through a hole formed in a part of aninterlayer insulation film 435. A pixel electrode 431 is also connectedto the active layer 432. The information about image modulation iswritten by turning on the polysilicon TFT 450, and by applying voltageto the liquid crystal sandwiched between the pixel electrode 431 and thecounter electrode. After completion of writing, the polysilicon TFT 450is turned off to keep the written information until the next informationis written.

However, since the polysilicon TFT liquid crystal panel is arranged sothat the side of the substrate 430 on which the polysilicon TFT isformed becomes the side of the cross-dichroic prism, the reflected lightfrom the cross-dichroic prism (return light) illuminates the polysiliconTFT liquid crystal panel from the direction indicated by arrows in thedrawing. When the reflected light reaches the active layer 432, acarrier due to light excitation is generated in the active layer 405,and a current (so-called optical leakage current) is produced althoughthe polysilicon TFT 450 is turned off. As a result, the voltage appliedto liquid crystal is changed, so that the state of image modulation isdisturbed.

The foregoing is the principle of occurrence of an incorrect operationof the polysilicon TFT liquid crystal light valve.

Incidentally, the optical leakage current tends to be produced whenlight of short wavelength is illuminated, and tends to be produced whenlight of high intensity (spectral) is illuminated.

That is, according to the former tendency, when the polysilicon TFTliquid crystal light valve is employed as the liquid crystal lightvalves 803, 805, 811, the incorrect operation of the light valve is mostsusceptible to the blue return light, and is relatively insusceptible tothe red return light. In this embodiment, the λ/4 phase plate 821 as thepolarization axis adjustment means is placed only between the blue lightliquid crystal light valve 811 and the cross-dichroic prism 813 on thebasis of such a tendency.

In addition, according to the latter tendency, of three color lights ofred, blue and green, the incorrect operation of the light valve issusceptible to the color light of relatively high intensity (spectral).Depending on the type of the light source 101 shown in FIG. 1, theintensity of the color light of a specific color may be higher than theintensity of light of other colors. For example, in general, in the caseof a metal halide lamp, the intensity of green light is relativelyhigher than the intensity of red and blue light. Therefore, in such acase, it is preferable to provide the polarization axis adjustment meansbetween the liquid crystal light valve 805 for green light and thecross-dichroic prism 813.

B. Second Embodiment

FIG. 8 illustrates the concept of the main part of a second embodiment.The second embodiment is such that in addition to the first embodimentshown in FIG. 5, blue light absorbing filters 841, 842 are provided onthe red light and green light incident surfaces of the cross-dichroicprism 813 so as to prevent unnecessary emergence of blue light from thecross-dichroic prism 813 to the red light Liquid crystal light valve 803and to the green light liquid crystal light valve 805. The basicoperation for projecting an image is exactly the same as the firstembodiment. Incidentally, in this embodiment, polarized light having apolarization axis in the direction perpendicular to the plane of thedrawing is referred to as the s-polarized light, and polarized lighthaving a polarization axis in the direction parallel to the plane of thedrawing is referred to as the p-polarized light.

Of the circularly polarized blue light emitted from the λ/4 phase plate821 to be incident on the cross-dichroic prism 813, unnecessarytransmitted light BRR transmitted by the red reflecting film 831 and bythe blue reflecting film 833, and unnecessary reflected light BRGreflected from the red reflecting film 831 and transmitted by the bluereflecting film 833 may be generated. The circularly polarized light issynthesized light of the s-polarized light and the p-polarized light,and when such transmitted light BRR and the reflected light BRG areilluminated without change on the emitting side of the surfaces of thered light liquid crystal light valve 803 and the green light liquidcrystal light valve 805, they are incident on the liquid crystal panels803b, 805b, passing through the p-polarized transmitting polarizingplates 803c, 805c, and an incorrect modulation of light is performed, sothat an incorrect image may be displayed. The blue light absorbingfilters 841, 842 absorb such transmitted light BRR and reflected lightBRG to prevent illumination on the liquid crystal light valves 803, 805.

In the second embodiment, not only the incidence of unnecessaryreflected light BRB on the blue light liquid crystal light valve 811 isprevented, but also unnecessary transmitted light BRR and the reflectedlight BRG, which may illuminate the red light liquid crystal light valve803 and the green light liquid crystal light valve 805, are absorbed bythe blue light absorbing filters 841, 842 to prevent the incorrectoperation of the projection display device.

C. Third Embodiment

FIG. 9 illustrates the concept of the main part of a third embodiment.The third embodiment is such that in addition to the first embodimentshown in FIG. 5, the λ/4 phase plates 823, 825 are further placed in theoptical paths between the red light liquid crystal light valve 803 andthe cross-dichroic prism 813, and between the green light liquid crystallight valve 805 and the cross-dichroic prism 813. Other components arethe same as those of the first embodiment. The p-polarized red lightmodulated by the red light liquid crystal light valve 803 to be emitted,and the p-polarized green light modulated by the green light liquidcrystal light valve 805 to be emitted are converted into circularlypolarized light by the λ/4 phase plates 823, 825 and are incident on thecross-dichroic prism 813, similarly to the blue light in the firstembodiment. However, the basic operation for projecting an image is thesame as that of the first embodiment.

In, the circularly polarized red light incident on the cross-dichroicprism 813, return light RRR reflected without being transmitted by theblue reflecting film 833, and incident again on the λ/4 phase plate 823is generated. Such return light is, similarly to the case shown in FIG.6, converted into s-polarized light to be emitted, and illuminates theside of the emitting surface of the red light liquid crystal light valve803. However, since the p-polarized transmitting polarizing plate 803c,which does not transmit the s-polarized light is provided on the side ofthe emitting surface of the red light liquid crystal light valve 803,the return light RRR converted into s-polarized light is not incident onthe liquid crystal panel 803b. Therefore, the influence of the redreturn light on the red light liquid crystal light valve 803 can beprevented. At this time, the optical axis of the λ/4 phase plate 823 maybe preferably set so that the emergent light thereof is converted intos-polarized light, when, of the circularly polarized blue light incidenton the cross-dichroic prism 813, the transmitted light BRR transmittedby both of the blue reflecting film 833 and the red reflecting film 831is incident on the λ/4 phase plate 823, as shown in FIG. 9.

This prevents the unnecessary blue reflected light BRR illuminated onthe red light liquid crystal light valve 803 from being incident on theliquid crystal panel 803b. Therefore, the influence of the unnecessaryblue transmitted light on the red light liquid crystal light valve 303can be prevented.

In addition, in regard to the green light emitted from the green lightliquid crystal light valve 805, return light CRG reflected toward thegreen light liquid crystal light valve 805 without being transmitted bythe red reflecting film 831 and the blue reflecting film 833 isgenerated. Such return light is also illuminated on the emitting sidesurface of the green light liquid crystal light valve 805 after beingconverted into s-polarized light, similarly to the above-describedreturn light RRR, BRB. However, since the p-polarized transmittingpolarizing plate 805c, which does not transmit the s-polarized light, isprovided on the emitting side surface of the green light liquid crystallight valve 805, the return light is not incident on the liquid crystalpanel 805b. Therefore, the influence of the unnecessary green reflectedlight on the green light liquid crystal light valve 805 can be alsoprevented. At this time, similarly to the above-described λ/4 phaseplate 823, the optical axis of the λ/4 phase plate 825 may be preferablyset so that of the circularly polarized blue light incident on thecross-dichroic prism 813, the reflected light BRG reflected from the redreflecting film 831 and transmitted by the blue reflecting film 833 isconverted into s-polarized light when it is incident on the λ/4 phaseplate 825. This prevents the unnecessary blue reflected light BRGilluminated on the green light liquid crystal light valve 805 from beingincident on the liquid crystal panel 305b. Therefore, the influence ofthe unnecessary blue reflected light on the green liquid crystal lightvalve 805 can be also prevented.

In the third embodiment, the λ/4 phase plates 823, 825, 821 are placedbetween the red light liquid crystal light valve 803, the green lightliquid crystal light valve 805, the blue light liquid crystal lightvalve 811 and the cross-dichroic prism 813, respectively, whereby notonly the red, green and blue return light generated in thecross-dichroic prism 813 is prevented from being incident on the liquidcrystal light valves 803, 805, 811 of the corresponding color andaffecting them, but also the unnecessary reflected light is preventedfrom being incident on other liquid crystal light valves 803, 811 andaffecting them.

In addition, in the third embodiment, since all the emergent lightemitted from the cross-dichroic prism 813 to the projection lens 814(FIG. 1) is circularly polarized light, not only a normal screen, butalso a polarizing screen can be used as the screen 815 for projectingthe projected image thereon.

D. Fourth Embodiment

FIG. 10 illustrates the concept of the main part of a fourth embodiment.The fourth embodiment is constituted such that a λ/2 phase plate 851 isplaced in the optical path between a blue light liquid crystal lightvalve 1811 and a cross-dichroic prism 834, and a λ/2 phase plate 852 isplaced in the optical path between a green light liquid crystal lightvalve 1805 and the cross-dichroic prism 834.

The λ/2 phase plates 851, 852 function as the polarization axisadjustment means. In addition, a blue-and-green-light-absorbing filter841a is provided on the red light incident surface of the cross-dichroicprism 834. In addition, in three liquid crystal light valves 1803, 1805,1811, p-polarized transmitting polarizing plates are used as polarizers1803a, 1805a, 1811a on the incident side surfaces of liquid crystalpanels 1803b, 1805b, 1811b, and s-polarized transmitting polarizingplates are used as polarizers 1803c, 1805c, 1811c on the emitting sideof the surfaces. Therefore, in the first embodiment, it is necessary toconvert the polarized light emitted from the polarizing beam splitterarray 320 into p-polarized light. This is made possible by moving theλ/2 phase plates shown in FIGS. 2 and 4 to the emitting surfaces of thes-polarized light reflected by the reflecting films 332.

Here, the optical axis of the λ/2 phase plate 851 is placed in thedirection to be inclined 22.5 degrees in a clockwise direction withrespect to the polarization axis of the s-polarized light passingthrough the s-polarized light transmitting polarizer 1811c. In addition,in order to reduce a decrease in quantity of the blue light as describedlater, it is assumed that the wavelength of the λ/2 phase plate 851 isset to the wavelength in which a blue spectrum shows a peak. At thistime, of the s-polarized blue light passing through the s-polarizedtransmitting polarizing plate 1811c, the return light BRB passingthrough the λ/2 phase plate 851 and reflected from the blue reflectingfilm 836 and the red reflecting film 835 of the cross-dichroic prism 834is incident on the λ/2 phase plate 851 again, and is converted intop-polarized light to illuminate the blue light liquid crystal lightvalve 1811.

FIG. 11 is a view for explaining this state. As described previously,the λ/2 phase plate 851 is placed so that its optical axis 851a has anangle of 22.5 degrees in a clockwise direction with respect tos-polarized light 860 (this angle is taken as θ1). When the s-polarizedlight 860 passes through the λ/2 phase plate 851, it becomes polarizedlight 861 having the inclination θ2 which is double the inclination θ1,i.e., the inclination rotated by 45 degrees in a clockwise direction. Apart of the polarized light 861 becomes return light BRB (polarizedlight 862) which is reflected from the blue reflecting film 836 and thered reflecting film 835 of the cross-dichroic prism 834 and is incidenton the λ/2 phase plate 851 again. The polarization axis of the polarizedlight 862 is the polarization axis symmetrical about a directionperpendicular to the plane of the drawing, i.e., the polarization axishaving the inclination θ3 rotated by 45 degrees in a counterclockwisedirection with respect to the s-polarized light 860. When the polarizedlight 862 passes through the λ/2 phase plate 851, it becomes polarizedlight 863 having the inclination θ5 which is double the angle θ4 formedbetween the polarized light 862 and the optical axis 851a, i.e., theinclination rotated by 135 degrees in a clockwise direction. Thepolarized light 863 is the polarized light in the directionperpendicular to the s-polarized light 860, i.e., the p-polarized light.That is, the return light BRB is converted into p-polarized light by theλ/2 phase plate 851 and illuminated on the blue light liquid crystallight valve 1811. However, since the s-polarized transmitting polarizingplate 1811c, which does not transmit the p-polarized light, is providedon the emitting side surface of the blue light liquid crystal lightvalve 1811, the return light BRB changed to p-polarized light isabsorbed by the s-polarized transmitting polarizing plate 1811c, and isnot incident on the Liquid crystal panel 1811b. Therefore, the influenceof the return light on the blue light liquid crystal light valve 1811can be prevented.

FIG. 12 is a graph showing an example of spectral distributioncharacteristics of a high-pressure discharge lamp used for the lightsource lamp 101 shown in FIG. 2. As such high pressure lamps, forexample, a halogen lamp, a metal halide lamp and so forth can bementioned. As shown in the drawing, a spectrum of each color has awavelength showing a peak. For example, the peaks are shown at λB, λG,and λR in the blue light, the green light and the red light,respectively. Therefore, the wavelength of the above-described λ/2 phaseplate 851 may be preferably set to the above wavelength λB in order totransmit the blue light most effectively and to reduce the decrease inquantity of light.

The polarized light 861 inclined 45 degrees in a clockwise directionwith respect to the s-polarized light (blue light) 860 is, as describedabove, incident on the blue reflecting film 836 of the cross-dichroicprism 834. This is due to the fact that an equal amount of p-polarizedlight and s-polarized light is incident. Therefore, in order to reflectefficiently the blue light incident on the cross-dichroic prism 834, itis necessary that both of the p-polarized blue light and the s-polarizedblue light are effectively reflected from the blue reflecting film 836.FIG. 13 is a graph showing examples of spectral reflectance of bluereflecting film 836. In FIG. 13, the reflectance characteristics withrespect to the s-polarized light are drawn by a broken line, and thereflectance characteristics with respect to the p-polarized light aredrawn by a solid line. Incidentally, a case where the reflectance is 50%or more is regarded as an effective reflection. The s-polarized lightshows effective reflection characteristics in a blue area of 400 to 500nm. On the other hand, the p-polarized light can only be effectivelyreflected within a range narrower than that of the s-polarized light.Thus, in order to realize the most efficient reflection of the bluelight, in the blue reflecting film 836, the reflectance of thep-polarized light is increased as high as possible, and the center ofthe reflection area is set to the wavelength λB showing the peak of theblue spectrum of the above-described lamp. This can effectively utilizeblue light of the lamp, and realize a projection display device ofbeautiful color.

Incidentally, examples of spectral reflectance of a conventional bluereflecting film are shown in FIG. 14. This reflecting film cannotreflect sufficiently the p-polarized light component, and a picturewhich is lacking in blue color is obtained.

The above-described cross-dichroic prism 834 having the blue reflectingfilm 836 is commonly composed of a dielectric multilayer film, and thecharacteristics thereof can be adjusted by changing dielectric materialsconstituting the multilayer film and by changing the number of layers ofthe multilayer film. In addition, in the first, second and thirdembodiments, the cross-dichroic prism 834 including the reflecting filmbest suited for characteristics of incident light may be preferablyused.

A description will be given returning to FIG. 10 again. The redreflecting film 835 has characteristics for reflecting green light tosome extent. Therefore, the reflected light GRB reflected from the redreflecting film 835 is incident on the blue light liquid crystal lightvalve 1811, whereby an incorrect operation may occur. Thus, in thisembodiment, the λ/2 phase plate 852 is also placed between the greenlight liquid crystal light valve 1805 and the cross-dichroic prism 834.The optical axis of the λ/2 phase plate 852 is placed to be inclined22.5 degrees in a counterclockwise direction with respect to thepolarization axis of the s-polarized light emitted from the green lightliquid crystal light valve 1805. Therefore, of the s-polarized lightemitted from the green light liquid crystal light valve 1805, thereflected light GRB reflected from the red reflecting film 835 isconverted into p-polarized light when passing through the λ/2 phaseplate 351. However, as described previously, since the s-polarizedtransmitting polarizing plate 1811c is provided on the emitting sidesurface of the blue light liquid crystal light valve 1811, thep-polarized light is absorbed by the s-polarized transmitting polarizingplate 1811c, and is not incident on the liquid crystal panel 1811b.Therefore, the influence of the unnecessary green reflected light on theblue light liquid crystal light valve 1811 can be prevented.

Incidentally, in this embodiment, a case is assumed where the influenceof the red light emitted from the red light liquid crystal light valve1803 on the liquid crystal light valves 1803, 1805, 1811 presents almostno problem. Therefore, as shown in FIG. 8, the λ/2 phase plate is notplaced in the optical path between the red light liquid crystal lightvalve 1803 and the cross-dichroic prism 834. When an incorrect operationdue to the red light is a problem, however, the λ/2 phase plate can beplaced there to avoid the problem.

In this embodiment, instead of providing the λ/2 phase plate between thered light liquid crystal light valve 1803 and the cross-dichroic prism834, a blue-and-green-light-absorbing filter 841a is provided on the redlight incident surface of the cross-dichroic prism 834. Theblue-and-green-light-absorbing filter 841a absorbs the transmitted lightBRR transmitted by the blue reflecting film 836 and the red reflectingfilm 835 within the cross-dichroic prism 834, and the reflected lightGRR transmitted by the red reflecting film 835 and reflected from theblue reflecting film so as to prevent the incidence on the red lightLiquid crystal light valve 1803.

Incidentally, in this embodiment, a description is given taking as anexample a case where the optical axis of the λ/2 phase plate is adjustedso that the s-polarized light incident on the λ/2 phase plate isconverted into linearly polarized light whose polarization axis isinclined 45 degrees with respect to a line of intersection of the bluereflecting film 836 and the red reflecting film 835 of thecross-dichroic prism 834. However, the adjustment is not limitedthereto. That is, the adjustment may be effected so that linearlypolarized light can be obtained in which the polarization axis of theemitted light from the λ/2 phase plate has a predetermined inclinationwith respect to the line of intersection of the blue reflecting film 836and the red reflecting film 835 of the cross-dichroic prism 834. Thisallows the return light incident on the cross-dichroic prism 834, andreflected from the blue reflecting film 835 and the red reflecting film336 to become linearly polarized light having a polarization axisinclination different from that of the emitted light from the λ/2 phaseplate. After passing through the λ/2 phase plate, this return lightbecomes linearly polarized light having a polarization axis inclinationdifferent from that of the linearly polarized light (s-polarized lightor p-polarized light) emitted from the liquid crystal light valves,i.e., the polarization axis inclined with respect to the polarizationaxis of the s-polarized light and to the polarization axis of thep-polarized light. Although the linearly polarized light having theinclined polarization axis is synthesized light of p-polarized light ands-polarized light, and includes both polarized light, the quantitiesthereof can be reduced as compared with a case where all the returnlight is polarized light having the same polarization axes as that ofthe emitted light from the liquid crystal light valves. This cansuppress an incorrect operation in the liquid crystal panels.

Particularly, the inclination of the polarization axis of the emittedlight from the λ/2 phase plate may be set within the range of about 10degrees to about 45 degrees with respect to the line of intersection ofthe blue reflecting film 836 and the red reflecting film 835 of thecross-dichroic prism 834. However, the range of 45 degrees to 90 degreesof the inclination of the polarization axis with respect to the line ofintersection is equivalent to the range of 45 degrees to 0 degrees, andthe above range of about 10 degrees to about 45 degrees is equivalent tothe range of about 80 degrees to about 45 degrees. This can reduce apolarization component in the polarization components of the returnlight (polarized light causing an incorrect operation) which is the sameas that of the emitted light from the liquid crystal light valves inresponse to the magnitude of the inclination. Incidentally, if theinclination of the polarization axis of the emitted light from the λ/2phase plate is set to about 10 degrees or more, the polarized lightcausing the incorrect operation can be reduced by about 10% or more.Further, if the above inclination range is set within the range of about22.5 degrees to 45 degrees, the ratio of the polarized light causing theincorrect operation in the polarization component of the return lightcan be reduced to about 50% or less, which is more effective. Inaddition, as described above, if the polarization axis of the emittedlight from the λ/2 phase plate is inclined about 45 degrees with respectto the line of intersection of the blue reflecting film 836 and the redreflecting film 835 of the cross-dichroic prism 834, the polarizationcomponent equal to that of the emitted light from the liquid crystallight valves can be substantially eliminated.

Further, although the λ/2 phase plate is used as the polarization axisadjustment means in the above embodiment, the means is not limitedthereto, and means may be employed as long as it can provide linearlypolarized light in which the polarization axis of the emitted light fromthe polarization axis adjustment means has a predetermined inclinationwith respect to the line of intersection of the blue reflecting film 836and the red reflecting film 835 of the cross-dichroic prism 834.

E. Fifth Embodiment

FIG. 15 illustrates the concept of the main part of a fifth embodiment.In this embodiment, the λ/2 phase plates 874, 875, 876 are placed on theside of the incident surfacers of three liquid crystal light valves 871,872, 873. The basic operation for projecting an image is the same asthat of the above described embodiments. Similarly to the firstembodiment shown in FIG. 1, the luminous flux emitted from the lightsource 10 is converted into one kind of linearly polarized light ofalmost uniform polarization directions by the polarized light generator20, and further, becomes s-polarized light split into each color. Then,each of the luminous flux split into colors red, green and blue areincident on the λ/2 phase plates 874, 875, 876 shown in FIG. 15. Theoptical axes of the λ/2 phase plates 874, 875, 876 are placed so as tobe inclined 22.5 degrees with respect to the s-polarized light.Therefore, the light emitted from the λ/2 phase plates 874, 875, 876becomes linearly polarized light whose polarization axis is rotated 45degrees in a clockwise direction.

Polarizing plates 871a, 872a, 873a on the incident side of the threeliquid crystal light valves 871, 872 and 873, respectively, are placedso that the transmission axes thereof coincide with the polarizationdirection of the incident light beam. In other words, these polarizers871a, 872a, 873a on the incident side merely increase the purity of thelinearly polarized light component similarly to the polarizers 803a,805a, 811a, and they can be omitted. Liquid crystal panels 871b, 872b,873b are panels using a twisted nematic liquid crystal twisted at 90degrees, and polarizers 871c, 872c, 873c thereof are placed so that thetransmission axes thereof are perpendicular to the transmission axes ofthe polarizers 871a, 872a, 873a on the incident side. Therefore, as oneexample shown in FIG. 16, from polarizers 871c, 872c, 873c on theemitting side, linearly polarized light is emitted which is inclined 45degrees with respect to the s-polarized light in the direction oppositeto the optical axes of the λ/2 phase plates 874, 875, 876.

Here, a subsequent action will be described taking the blue light as anexample. The linearly polarized light emitted from the polarizer 873c onthe emitting side is linearly polarized light 873d in which an equalamount of the s-polarized light component and p-polarized lightcomponent is synthesized. The linearly polarized light 873d is incidenton a cross-dichroic prism 884, almost entirely reflected from a bluereflecting film 886 and then, transmitted by a red reflecting film 885.Here, although it is in small quantity, return light BRB which isreflected from the red reflecting film 835 and returns to the blue lightliquid crystal light valve 873 is generated. However, this reflectedlight BRB is linearly polarized light in the direction perpendicular tothe transmission axis of the polarizer 873c, and is entirely absorbed bythe polarizer 873c. Therefore, the return light BRB is not incident onthe liquid crystal panel 873b, so that an incorrect operation can beprevented. Return light of other colors can be prevented similarly.Incidentally, as the cross-dichroic prism 884, the cross-dichroic prism813 of the third embodiment can be used.

In addition, in the linearly polarized light emitted from the polarizer873c, transmitted light (transmitted light BTR) which is transmittedstraight by the cross-dichroic prism 884 to be incident on the polarizer871c of the red light liquid crystal light valve 871 is included.However, as is apparent form FIG. 15, since the polarizer 871c is placedso that the transmission axis thereof is perpendicular to thetransmission axis of the polarizer 873c, the transmitted light BTR isabsorbed by the polarizer 871c. Therefore, the transmitted light BTR isnot incident on the liquid crystal panel 871b, and the incorrectoperation caused thereby can be prevented.

Further, as is apparent from FIG. 15, since the polarizer 872c on theemitting side of the green light liquid crystal light valve 872 isplaced so that the transmission axis thereof is perpendicular to thetransmission axis of the blue polarizer 873c, the incorrect operation ofthe blue light liquid crystal light valve 873 due to the influence ofthe green light can be prevented.

Incidentally, in this embodiment, a description is given taking as anexample a case where the optical axis of the λ/2 phase plate is adjustedso that the s-polarized light incident on the λ/2 phase plate isconverted into linearly polarized light in which the polarization axisthereof is inclined 45 degrees with respect to the line of intersectionof the blue reflecting film 836 and the red reflecting film 835 of thecross-dichroic prism 834. However, the adjustment is not limitedthereto. The adjustment may be effected so that linearly polarized lightcan be obtained in which the polarization axis of the emitted light fromthe λ/2 phase plate has a predetermined inclination with respect to theline of intersection of the blue reflecting film 836 and the redreflecting film 835, and a polarizer may be provided so that thepolarization axis of the linearly polarized light emitted from thepolarizer on the emitting side of the liquid crystal light valve has apredetermined angle with respect to the line of intersection of the bluereflecting film 836 and the red reflecting film 835. This allows thereturn light incident on the cross-dichroic prism 834 and reflected fromthe blue reflecting film 836 and the red reflecting film 835 to becomelinearly polarized light having a polarization axis inclinationdifferent from that of the emitted light from the polarizer on theemitting side of the liquid crystal light valve. When the inclination ofthe polarization axis of the emitted light from the λ/2 phase plate isnot substantially 45 degrees, the inclination of the polarization axisof the return light is different from that of the absorption axis of thepolarizer on the emitting side of the liquid crystal light valve, sothat the return light cannot be completely absorbed. However, thequantity thereof can be reduced as compared with a case where all thereturn light is polarized light having a polarization axis in the samedirection as that of the transmission axis of the polarizer on theemitting side of the liquid crystal light valve. This can suppress theincorrect operation in the liquid crystal panels.

For example, the inclination of the polarization axis of the emittedlight from the λ/2 phase plate may be set to any angle in the range ofabout 10 degrees to 45 degrees with respect to the line of intersectionof the blue reflecting film 836 and the red reflecting film 835 of thecross-dichroic prism 834, and the inclination of the polarization axisof the emitted light from the polarizer on the emitting side of theliquid crystal light valve may be set substantially equal to orperpendicular to the inclination of the polarization axis of the emittedlight from the λ/2 phase plate. However, the range of 45 degrees to 90degrees of the inclination of the polarization axis with respect to theline of intersection is equivalent to the range of 45 degrees to 0degree, and the above range of about 10 degrees to about 45 degrees isequivalent to the range of about 80 degrees to about 45 degrees. Thiscan reduce a polarization component in the polarization components ofthe return light (polarized light causing an incorrect operation), whichis the same as that of the emitted light from the liquid crystal lightvalve in response to the magnitude of the inclination. Incidentally, ifthe inclination of the polarization axis of the emergent light from theλ/2 phase plate is set about 10 degrees or more, the polarized lightcausing the incorrect operation can be reduced by about 10% or more.Further, if the above inclination range is set within the range of about22.5 degrees to 45 degrees, the ratio of the polarized light causing theincorrect operation in the polarization components of the return lightcan be reduced to about 50% or less, which is more effective. Inaddition, as described above, if the polarization axis of the emittedlight from the λ/2 phase plate is inclined about 45 degrees, thepolarization component equal to that of the emitted light from thepolarizer on the emitting side of the liquid crystal light valve can besubstantially eliminated.

Further, although the λ/2 phase plate is used as the polarization axisadjustment means in the above embodiment, the means is not limitedthereto, and means may be employed as long as it can provide linearlypolarized light in which the polarization axis of the emitted light fromthe polarization axis adjustment means has a predetermined inclinationwith respect to the line of intersection of the blue reflecting film 836and the red reflecting film 835 of the cross-dichroic prism 834.

The present invention is not limited to the above embodiments and modesfor carrying out the invention, and is capable of being carried out invarious forms within the spirit and scope thereof. For example, thefollowing modifications may be performed.

(1) Although the green light is transmitted straight through by thecross-dichroic prism 813 in the above-described first to thirdembodiments, there is no need for the light to be limited thereto, andthe red light or the blue light may be transmitted straight through.

(2) In the above-described first to third embodiments, an example ofpreventing an incorrect operation of the liquid crystal light valveusing the λ/4 phase plate is shown. In addition, in the fourth to fifthembodiments, an example of preventing the incorrect operation of theliquid crystal light valve by the λ/2 phase plate and the polarizersincluded in the liquid crystal light valve is shown. Further, an exampleof preventing the incorrect operation by absorbing filters is shown. Inaddition, an example of the cross-dichroic prism is shown as color lightsynthesizing means. However, there is no need for the prevention of theincorrect operation to be limited thereto, and in the case ofsynthesizing color light using red, green and blue liquid crystal lightvalves, the incorrect operation may be prevented by the combination ofphase plates, polarizers, and absorbing filters and so forth.

(3) In this embodiment, although a description is given laying stress onthe incorrect operation of the liquid crystal light valve due to theblue light, there is no need to be limited thereto. A polarization axisadjustment means, such as a λ/2 phase plate and a λ/4 phase plate may bepreferably included so as to prevent the incorrect operation in theliquid crystal light valve due to color light whose sensitivity of amodulation control element for performing modulation of light in theliquid crystal light valve is high. In addition, polarization axisadjustment means, such as a λ/2 phase plate and a λ/4 phase plate may bepreferably included so as to prevent the incorrect operation due to thecolor light having a relatively high spectral intensity in each colorlight, i.e., the color light showing a relatively high peak among thespectral peaks of each color light.

(4) In the first to fifth embodiments, a description is given with eachincident color light limited to linearly polarized light consisting ofone polarization component (s-polarized light or p-polarized light).However, if the light having two mixed components of light is employedas the incident light, a similar action and effect can be obtained.

What is claimed is:
 1. A projector, comprising:a light source; a colorseparator that separates light from said light source into first, secondand third color light; first, second, and third optical modulators thatrespectively modulate said first, second, and third color light on thebasis of a given image signal to emit first, second, and third modulatedlight, respectively, which are predetermined linearly polarized light; acolor light synthesizer that synthesizes said first, second and thirdmodulated light, said color light synthesizer having a first reflectingfilm that reflects said first color light, and a second reflecting filmthat reflects said third color light, said first reflecting film andsaid second reflecting film being arranged in an X shape; a polarizationaxis adjustment device provided between at least one of said first,second and third optical modulators and said color light synthesizer,said polarization axis adjustment device converting the linearlypolarized light into circularly polarized light; and a polarizerdisposed between the at least one modulator and said polarization axisadjustment device.
 2. The projector as claimed in claim 1, wherein saidpolarization axis adjustment device is a λ/4 phase plate.
 3. Theprojector as claimed in claim 1, further comprising a modulation controlelement formed in said optical modulators, said polarization axisadjustment device being provided between said optical modulators andsaid color light synthesizer for color light of relatively shortwavelength among said first, second and third color light.
 4. Theprojector as claimed in claim 1, said polarization axis adjustmentdevice being provided between said optical modulators and said colorlight synthesizer for color light having a relatively high spectralintensity among said first, second and third color light.
 5. Aprojector, comprising:a light source; a color separator that separateslight from said light source into first, second and third color light;first, second, and third optical modulators that respectively modulatesaid first, second, and third color light on the basis of a given imagesignal to emit first, second, and third modulated light, respectively,which are predetermined linearly polarized light; a color lightsynthesizer that synthesizes said first, second and third modulatedlight, said color light synthesizer having a first reflecting film thatreflects said first color light, and a second reflecting film thatreflects said third color light, said first reflecting film and saidsecond reflecting film being arranged in an X shape; a polarization axisadjustment device provided between at least one of said first, secondand third optical modulators and said color light synthesizer, saidpolarization axis adjustment device being a λ/2 phase plate andadjusting the polarization axis of the linearly polarized light to apredetermined angle with respect to a line of intersection of said firstreflecting film and said second reflecting film, said predeterminedangle being an angle in the range of about 10 degrees to about 45degrees; and a polarizer disposed between the at least one modulator andsaid polarization axis adjustment device.
 6. The projector as claimed inclaim 5, wherein said predetermined angle is about 45 degrees.
 7. Theprojector as claimed in claim 5, further comprising a modulation controlelement formed in said optical modulators, said polarization axisadjustment device being provided between said optical modulators andsaid color light synthesizer for color light of relatively shortwavelength among said first, second and third color light.
 8. Theprojector as claimed in claim 5, said polarization axis adjustmentdevice being provided between said optical modulators and said colorlight synthesizer for color light having a relatively high spectralintensity among said first, second and third color light.
 9. Aprojector, comprising:a light source; a color separator that separateslight from said light source into first, second and third color light;first, second, and third optical modulators that respectively modulatesaid first, second, and third color light on the basis of a given imagesignal to emit first, second, and third modulated light, respectively,which are predetermined linearly polarized light; a color lightsynthesizer that synthesizes said first, second and third modulatedlight, said color light synthesizer having a first reflecting film thatreflects said first color light, and a second reflecting film thatreflects said third color light, said first reflecting film and saidsecond reflecting film being arranged in an X shape; a polarization axisadjustment device that adjusts a polarization axis of the linearlypolarized light to a first predetermined angle with respect to a line ofintersection of said first reflecting film and said second reflectingfilm, the polarization axis adjustment device being provided betweensaid light source and at least one of said first, second, and thirdoptical modulators; and a polarizer provided on an emitting side surfaceof said optical modulators corresponding to said polarization axisadjustment device, the polarizer transmitting only linearly polarizedlight emitted from said optical modulators having a polarization axis ofa predetermined second angle with respect to a line of intersection ofsaid first reflecting film and said second reflecting film, wherein saidfirst angle is an angle in the range of about 10 degrees to about 45degrees, and said second angle is substantially equal to said firstangle or different from said first angle by approximately 90 degrees.10. The projector as claimed in claim 9, wherein said polarization axisadjustment device is a λ/2 phase plate.
 11. The projector as claimed inclaim 9, wherein said first angle is about 45 degrees.
 12. A projector,comprising:a light source; a color separator that separates light fromsaid light source into first, second and third color light; first,second, and third optical modulators that respectively modulate saidfirst, second, and third color light on the basis of a given imagesignal to emit first, second, and third modulated light, respectively,which are predetermined linearly polarized light; a color lightsynthesizer that synthesizes said first, second and third modulatedlight, said color light synthesizer having a first reflecting film thatreflects said first color light, and a second reflecting film thatreflects said third color light, said first reflecting film and saidsecond reflecting film being arranged in an X shape; a polarization axisadjustment device provided between at least one of said first, secondand third optical modulators and said color light synthesizer; apolarizer disposed between the at least one modulator and saidpolarization axis adjustment device; and a color absorption device thatabsorbs only color light passing through said polarization axisadjustment device, the color absorption device being provided in anoptical path between said optical modulators and said light synthesizerwhere said polarization axis adjustment device is not provided, saidpolarization axis adjustment device being placed on only one or twooptical axis.
 13. The projector as claimed in claim 12, furthercomprising a modulation control element formed in said opticalmodulators, said polarization axis adjustment device being providedbetween said optical modulators and said color light synthesizer forcolor light of relatively short wavelength among said first, second andthird color light.
 14. The projector as claimed in claim 12, saidpolarization axis adjustment device being provided between said opticalmodulators and said color light synthesizer for color light having arelatively high spectral intensity among said first, second and thirdcolor light.
 15. The projector as claimed in claim 9, further comprisinga color absorption device that absorbs only color light passing throughsaid polarization axis adjustment device, the color absorption devicebeing provided in an optical path between said optical modulators andsaid light synthesizer where said polarization axis adjustment device isnot provided, said polarization axis adjustment device being placed ononly one or two optical axis.